The present invention relates to broadcast antennas. More particularly, the present invention relates to a system and method for utilizing a single feed line for feeding multiple broadcast antennas.
In response to the federal mandate requiring a transition from NTSC television transmission to digital television (xe2x80x9cDTVxe2x80x9d) transmission, and the need to continue providing NTSC service, broadcasters have begun adding DTV antennas to existing antenna towers. Due to the limited number of existing antenna towers and, owing to the geographical limitations imposed by xe2x80x9cline of sightxe2x80x9d transmission requirements, the limited locations available in many areas for additional towers the addition of antennas is not without problems.
A first problem resulting from the transition to DTV is the limited amount of xe2x80x9creal estatexe2x80x9d on existing towers. A tower on which a DTV antenna is to be added is likely to have a number of UHF and VHF antennas already mounted on it along with a number of AM, FM and cellular telephone antennas. Continual efforts are being made to improve the design of antennas to reduce size to decrease weight and wind load. By reducing weight and wind load, an increased number of antennas can be mounted on existing towers.
A second problem that exists is that, under existing practices, each antenna is fed by a separate feed line. The feed lines can be of the wave guide or coaxial structure type but the coaxial structure type is preferred as it causes less wind load and does not cause group delay distortion on the signal as does a waveguide structure. Notwithstanding this, because the coaxial feed lines are required to handle high power, e.g., 50 kW, the inner and outer conductors must be sufficiently large to handle this load and thus still cause significant wind load
While improvements in antenna design can greatly increase the number of antennas that can be supported by a tower, it would be beneficial to be able to feed multiple antennas utilizing a single feed line thereby further increasing the wind load capacity of the tower. As described below, attempts have been made to solve this problem.
U.S. Pat. No. 5,774,193 uses a signal combiner to combine the NTSC and DTV signals to form a composite signal that is fed up the transmission line. A signal separator disposed at the upper end of the transmission line separates the composite signal into the DTV signal and NTSC signal for application to the DTV and NTSC antennas. The signal separator is formed of a high pass filter and a low pass filter. The high pass filter passes an ultra high frequency (UHF) DTV signal to the DTV antenna, but rejects a very high frequency (VHF) NTSC signal. The low pass filter passes the VHF NTSC signal to the NTSC antenna, but rejects the UHF DTV signal. The high and low pass filter separator may provide adequate bandwidth and rejection for the case of the DTV signal and the NTSC signal being in two different frequency bands. However, it does not provide adequate rejection for the case where the carrier frequencies of the two signals are relatively close together as, for example, in the same frequency band. Another problem which exists in the foregoing system is the significant additional wind load caused by the high pass filter cross section.
It would therefore be advantageous to provide an antenna feed system capable of feeding more than one antenna with a single feed line that does not require the use of a high pass filter.
The foregoing needs have been satisfied to a great extent by the present invention which, in one aspect, is a broadcast antenna feed system. The feed system includes a tower antenna feed line and a signal splitter having a first terminal connected to the tower antenna feed line. A first antenna is connected to a second terminal of the splitter and a second antenna is connected to a third terminal of the splitter. The first antenna is tuned to a first carrier frequency and the second antenna is tuned to a second carrier frequency.
The splitter includes a first filter for filtering signals to the first antenna and a second filter for filtering signals to the second antenna. The filters can be bandpass filters, lowpass filters, or band notch filters depending on what type of signals are combined in the signal transmitted to the splitter over the feed line.
In another aspect of the invention, an antenna feed system is provided which includes feeder means for transmitting a feed signal containing first and second broadcast signals to a splitter means. The splitter means is connected to the feeder means to separate out a first and second broadcast transmission signal from the feed signal. A first transmission means and a second transmission means on a broadcast tower are also provided for, respectively, transmitting the first and second broadcast transmission signals.
In yet another aspect of the invention, a method of feeding broadcast antennas is provided. The method includes the steps of feeding a signal containing first and second broadcast signals to a splitter on an antenna tower. The signal is then split into a first and second broadcast transmission signal at the splitter. The first broadcast signal is transmitted over a first antenna and the second broadcast signal is transmitted over a second antenna.
There has been outlined, rather broadly, the more important features of the invention in order that the detailed description thereof that follows may be better understood, and in order that the present contribution to the art may be better appreciated. There are, of course, additional features of the invention that will be described below and which will form the subject matter of the claims appended hereto.
In this respect, before explaining at least one embodiment of the invention in detail, it is to be understood that the invention is not limited in its application to the details of construction and to the arrangements of the components set forth in the following description or illustrated in the drawings. The invention is capable of other embodiments and of being practiced and carried out in various ways. Also, it is to be understood that the phraseology and terminology employed herein, as well as the abstract, are for the purposes of description and should not be regarded as limiting.
As such, those skilled in the art will appreciate that the conception upon which this disclosure is based may readily be utilized as a basis for the designing of other structures, methods and systems for carrying out the several purposes of the present invention. It is important, therefore, that the claims be regarded as including such equivalent construction insofar as they do not depart from the spirit and scope of the present invention.